1. Field of the Invention
This invention relates to triphenylphosphine which is useful in polyene synthesis.
2. Description of the Prior Art
Triphenylphosphine can be recovered by the regeneration of triphenylphosphine oxide resulting from a polyene synthesis.
In a prior art process for recovering triphenylphosphine, triphenylphosphosphine oxide was reacted with phosgene in chloroform to give a triphenylphosphine dichloride-chloroform adduct of the formula (C.sub.6 H.sub.5).sub.3 PCl.sub.2.CHCl.sub.3. The adduct was then reduced to triphenylphosphine by heating same with white phosphorous. This prior art process suffered from the disadvantages associated with the use of phosphorous, such as the poisonous nature of phosphorous. Furthermore, when using phosphorous, air must be riqorously excluded.
In another prior art process for recovering triphenylphosphine, triphenylphosphine oxide was reacted (i.e. chlorinated) with phosgene and the resulting triphenylphosphine dichloride was reduced to the desired product. In this prior art process, the chlorination of triphenylphosphine oxide was carried out in a solvent, such as a chlorinated hydrocarbon solvent (e.g. carbon tetrachloride) and the reduction of the resulting triphenylphosphine dichloride was carried out by using hydrogen in toluene. It was of great importance to completely remove the carbon tetrachloride solvent from the triphenylphosphine dichloride obtained in the reaction with phosgene before initiating reduction. The carbon tetrachloride otherwise would react with the triphenylphosphine produced by the reduction and thereby decrease the yield of the desired product. Accordingly, this prior art process disadvantageously compelled the laborious removal of the solvent from the triphenylphosphine dichloride intermediate product.
I have invented a process for producing triphenylphosphine which avoids the disadvantages of the above described prior art processes by utilizing chloroform as the solvent in the chlorination reaction. With the process of the invention, it is no longer necessary to remove the solvent used in the chlorination (adduct forming) step, before initiating the reduction step. I have also found that chloroform is a better solvent than toluene for the reduction of triphenylphosphine dichloride to triphenylphosphine. Methylene chloride and carbon tetrachloride are unsuitable for this reduction (hydrogenolysis).